Although larger doses of alcohol lead to more severe symptoms, hangover is not solely dose-related. Acetaldehyde, the dehydrogenated product of alcohol metabolism, might be responsible for hangover symptoms. Congeners, the byproducts of individual alcohol preparations (which are found primarily in brandy, wine, tequila, whiskey, and other dark liquors), increase the frequency and severity of hangover. Clear liquors, such as rum, vodka, and gin, tend to cause hangover less frequently, which may explain why patients with chronic alcoholism use these liquors disproportionately. In an experimental setting, 33% of patients who consumed 1.5 g/kg of body weight of bourbon (which has high congeners) but only 3% of those who consumed the same dose of vodka (which has low congeners) experienced severe hangover.
—Jeffrey G. Wiese, Michael G. Shlipak, and Warren S. Browner, “The Alcohol Hangover”, Annals of Internal Medicine, vol. 132 no. 11, 6 June 2000, pp. 897-902, at p. 899

If true, this observation cuts across the Russian distinction between intoxication (интоксикация) by alcohol and hangover (похмелье) construed as withdrawal from that toxic substance. Stateside, hangovers are the province of alcoholic dilettanti, as per their R—E—M—O—R—S—E, immortalized by George Ade. Furthermore, the ease of consumption attributed to good vodka by good Russians, is in all likelihood also due to the lack of fusel oils.